Today's technology bubble is worse than the one that burst 15 years ago, according to billionaire entrepreneur Mark Cuban.

Overvalued tech companies today are mostly private rather than publicly traded, he wrote in a Wednesday blog post. That distinction makes torrents of funding more dangerous for investors, Cuban contended.

"Back then the companies the general public was investing in were public companies. They may have been horrible companies, but being public meant that investors had liquidity to sell their stocks," the Dallas Mavericks owner and "Shark Tank" investor wrote.

"The bubble today comes from private investors who are investing in apps and small tech companies," Cuban continued.

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Mark Cuban

The post comes two days after the Nasdaq hit 5,000 for the first time since the tech bubble of 2000. This time, though, Cuban isn't worried about public companies.

Cuban believes that angel investors and other private investors make more perilous plays than stock traders 15 years ago. Those investments lack the liquidity that a stock investment would have, he said.

Cuban asked: "If a stock in a company is worth what somebody will pay for it, what is the stock of a company worth when there is no place to sell it?"